There are specific authors whose books send me into withdrawal after finishing them – JK Rowling is definitely one of them; Orson Scott Card is another. After reading one of their books, I have to take a couple of days off before starting another book, because other authors just don’t live up to the quality of writing I’ve gotten used to…
I was especially sad after the last Harry Potter book too, not knowing if there would be more JKR books in the future; fortunately, Orson Scott Card comes out with a new book every year or so, so I can get my fix!